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1.
J Nanosci Nanotechnol ; 11(4): 3151-61, 2011 Apr.
Article in English | MEDLINE | ID: mdl-21776682

ABSTRACT

The microphase-separation of Langmuir-Blodgett (LB) monolayers of a rhodamine B (RhB) end-labeled double hydrophilic block copolymer (DHBC), RhB-Poly(N,N-dimethylacrylamide)-b-poly(N,N-diethylacryl-amide) (RhB-PDMA(207)b-PDEA177) and the 1:1 segmental mixture of PDEA and RhB-PDMA homopolymers was followed by AFM. The DHBC LB films revealed a loose distribution of nano-aggregates with variable geometries below the lower critical solution temperature (LCST) of PDEA (32 degrees C) and low surface pressure (3 mN m(-1)). By increasing either the temperature above the LCST of PDEA or the surface pressure beyond the immersion regime of PDMA in the subphase (7 mN m(-1)) a dense nanopatterning was obtained. The absence of a corresponding regular nanopatterning in LB films of mixed homopolymers with the same composition highlights the role of the covalent bonding between PDEA and PDMA on the self-segregation of the two blocks at the air-water interface.


Subject(s)
Membranes, Artificial , Microscopy, Atomic Force/methods , Nanostructures/chemistry , Nanostructures/ultrastructure , Polymethacrylic Acids/chemistry , Materials Testing , Particle Size , Surface Properties , Temperature
2.
Langmuir ; 26(22): 17165-77, 2010 Nov 16.
Article in English | MEDLINE | ID: mdl-20964300

ABSTRACT

Phase separation and interactions in mixed monolayers of dipalmitoylphosphatidylglycerol (DPPG) with the rhodamine B end-labeled double-hydrophilic block copolymer (DHBC), poly(N,N-dimethylacrylamide)-block-poly(N,N-diethylacrylamide) (RhB-PDMA(207)-b-PDEA(177)), was studied at the air-water interface. Surface pressure versus area isotherms indicate that both components behave almost independently. Brewster angle microscopy (BAM) images show a random distribution of liquid condensed (LC) domains of DPPG in an apparent homogeneous matrix of DHBC, excluding the macroscopic phase separation. The laser scanning confocal fluorescence microscopy (LSCFM) of the rhodamine dye at the end of the PDMA chain showed how the DHBC is distributed in Langmuir-Blodgett (LB) mixed monolayers. The high spatial resolution of atomic force microscopy (AFM) combined with the LCSFM images indicates that DHBC incorporates in the expanded phase of DPPG to form mixed domains, being excluded from the condensed regions. Upon compression, nanosized LC domains of DPPG nucleate inside the mixed domains corralled in the nanopatterning of pure DHBC. The negatively charged polar group of DPPG inhibits rhodamine aggregation, while the long polymer chains promote the formation of corralled nanodomains of DPPG in two dimensions.


Subject(s)
Acrylamides/chemistry , Air , Hydrophobic and Hydrophilic Interactions , Microscopy, Atomic Force/methods , Microscopy, Confocal/methods , Phosphatidylglycerols/chemistry , Water/chemistry , Rhodamines/chemistry , Temperature
3.
Langmuir ; 26(3): 1807-15, 2010 Feb 02.
Article in English | MEDLINE | ID: mdl-19928784

ABSTRACT

The thermoresponsive behavior of the rhodamine B end-labeled double hydrophilic block copolymer (DHBC) poly(N,N-dimethylacrylamide)-b-poly(N,N-diethylacrylamide) (RhB-PDMA(207)-b-PDEA(177)) and the 1:1 segmental mixture of PDEA and rhodamine B end-labeled PDMA homopolymers was studied over the range of 10-40 degrees C at the air-water interface. The increase in collapse surface pressure (second plateau regime) of the DHBC with temperature confirms the thermoresponsiveness of PDEA at the interface. The sum of the pi-A isotherms of the two single homopolymers weighted by composition closely follows the pi-A isotherm of the DHBC, suggesting that the behavior of each block of the DHBC is not influenced by the presence of the other block. Langmuir-Blodgett monolayers of DHBC deposited on glass substrates were analyzed by laser scanning confocal fluorescence microscopy (LSCFM), showing schizophrenic behavior: at low temperature, the RhB-PDMA block dominates the inside of bright (core) microdomains, switching to the outside (shell) at temperatures above the lower critical solution temperature (LCST) of PDEA. This core-shell inversion triggered by the temperature increase was not detected in the homopolymer mixture. The present results suggest that both the covalent bond between the two blocks of the DHBC and the tendency of rhodamine B to aggregate play a role in the formation of the bright cores at low temperature whereas PDEA thermoaggregation is responsible for the formation of the dark cores above the LCST of PDEA.


Subject(s)
Acrylamides/chemistry , Air , Temperature , Water/chemistry , Hydrophobic and Hydrophilic Interactions , Microscopy, Confocal , Pressure , Rhodamines/chemistry , Surface Properties
4.
Phys Chem Chem Phys ; 7(22): 3874-83, 2005 Nov 21.
Article in English | MEDLINE | ID: mdl-16358039

ABSTRACT

Langmuir monolayers (LM) and Langmuir-Blodgett (LB) films of pure lipophilic meso-tetra(4-dodecylaminosulfophenyl)porphyrin (PC12) and mixed with the anionic surfactant sodium hexadecylsulfate (SHS) were studied. The molecular packing and structure of PC12 and PC12-4SHS with variable surface pressure were investigated by surface pressure-area measurements, steady-state absorption, fluorescence emission and anisotropy, as well as by fluorescence lifetime imaging microscopy (FLIM). At low surface pressure, the porphyrin molecules are organized with the rings tilted on the water surface whereas at high surface pressure the porphyrin rings achieve a more perpendicular arrangement. Using the FLIM images a gradual change of aggregates into large "islands" is observed. Different patterns are observed in the pure PC12 multilayer films (n = 3 and 5) with ordered patches superimposed which are not observed in the PC12-4SHS multilayer LB films.


Subject(s)
Porphyrins/chemistry , Sulfonamides/chemistry , Chemical Phenomena , Chemistry, Physical , Microscopy, Fluorescence , Models, Molecular , Molecular Structure , Porphyrins/metabolism , Sulfonamides/metabolism , Surface Properties
5.
Chem Phys Lipids ; 137(1-2): 62-76, 2005 Oct.
Article in English | MEDLINE | ID: mdl-16095583

ABSTRACT

The behaviour of binary mixtures involving dipalmitoylphosphatidylcholine (DPPC), dioctadecyldimethylammonium bromide (DODAB) and oleic acid (OA) was investigated at the air-water interface by surface pressure-area (pi-A) measurements and by Brewster angle microscopy (BAM). Thermodynamic analysis indicates for the system DPPC/DODAB miscibility with strong negative deviations from the ideal behaviour, from low to high surface pressures over all the composition range. For systems DODAB/OA and DPPC/OA, thermodynamic analysis and BAM observation indicate miscibility from low to intermediate surface pressures, and phase separation in a limited range of composition at high surface pressures. The interaction of nicotinic acid (NA) with pure lipids and with selected compositions of mixed systems was investigated. Significant positive deviations of pi-A isotherms in the presence of NA indicate attractive interactions between NA and the polar groups of DPPC and DODAB. NA easily penetrates in expanded regimes while it tends to be segregated from condensed regimes in mixed monolayers.


Subject(s)
1,2-Dipalmitoylphosphatidylcholine/chemistry , Niacin/chemistry , Oleic Acid/chemistry , Quaternary Ammonium Compounds/chemistry , Air , Membranes, Artificial , Microscopy , Surface Properties , Thermodynamics , Water/chemistry
6.
Chem Phys Lipids ; 131(1): 27-39, 2004 Aug.
Article in English | MEDLINE | ID: mdl-15210362

ABSTRACT

The behaviour of dipalmitoylphosphatidylcholine (DPPC), mixed with stearonitrile (SN), was investigated at the air-water interface by surface pressure-area (pi-A) measurements and by direct visualisation of monolayers by Brewster angle microscopy (BAM). The pi-A-X diagram of system DPPC/SN was compared with the corresponding diagrams of systems DPPC/stearic acid (SA) and DPPC/octadecanol (OD) at 20 degrees C. Monolayers of the three systems reach the closest packing of alkyl chains in the 0.4-0.6 range of XDPPC. Thermodynamic analysis indicates miscibility in the three binary systems with negative deviations from the ideal behaviour. Morphological features of system DPPC/SN change significantly with XDPPC and temperature in the range 10-30 degrees C. At 10 and 20 degrees C mixed monolayers form condensed states from low pi all over the composition range. At 30 degrees C, the liquid-expanded (LE)--liquid-condensed (LC) phase transition occurs at increasing pi with XDPPC. The shape and size of condensed domains change with XDPPC and pi. Contrarily to the behaviour of pure components, mixed monolayers of DPPC/SN exhibit orientational order in the 0.2-0.6 mol fraction range of DPPC. BAM observation confirmed the partial miscibility indicated by GE data in a limited range of compositions at 30 degrees C.


Subject(s)
1,2-Dipalmitoylphosphatidylcholine/chemistry , Air , Fatty Alcohols/chemistry , Nitriles/chemistry , Stearic Acids/chemistry , Water , Biophysical Phenomena , Biophysics , Membranes, Artificial , Microscopy, Fluorescence , Phase Transition , Pressure , Surface Properties , Temperature
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